2 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
3 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License, version 2 only,
7 * as published by the Free Software Foundation.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License along
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
24 #include <sys/types.h>
29 #include <common/error.h>
34 * Using fork to set umask in the child process (not multi-thread safe). We
35 * deal with the shm_open vs ftruncate race (happening when the sessiond owns
36 * the shm and does not let everybody modify it, to ensure safety against
37 * shm_unlink) by simply letting the mmap fail and retrying after a few
38 * seconds. For global shm, everybody has rw access to it until the sessiond
41 static int get_wait_shm(char *shm_path
, size_t mmap_size
, int global
)
48 /* Default permissions */
49 mode
= S_IRUSR
| S_IWUSR
| S_IRGRP
| S_IWGRP
;
51 /* Change owner of the shm path */
53 ret
= chown(shm_path
, 0, 0);
55 if (errno
!= ENOENT
) {
56 PERROR("chown wait shm");
62 * If global session daemon, any application can register so the shm
63 * needs to be set in read-only mode for others.
67 ret
= chown(shm_path
, getuid(), getgid());
69 if (errno
!= ENOENT
) {
70 PERROR("chown wait shm");
77 * Set permissions to the shm even if we did not create the shm.
79 ret
= chmod(shm_path
, mode
);
81 if (errno
!= ENOENT
) {
82 PERROR("chmod wait shm");
88 * We're alone in a child process, so we can modify the process-wide
94 * Try creating shm (or get rw access). We don't do an exclusive open,
95 * because we allow other processes to create+ftruncate it concurrently.
97 wait_shm_fd
= shm_open(shm_path
, O_RDWR
| O_CREAT
, mode
);
98 if (wait_shm_fd
< 0) {
99 PERROR("shm_open wait shm");
103 ret
= ftruncate(wait_shm_fd
, mmap_size
);
105 PERROR("ftruncate wait shm");
110 ret
= fchmod(wait_shm_fd
, mode
);
116 #warning "FreeBSD does not support setting file mode on shm FD. Remember that for secure use, lttng-sessiond should be started before applications linked on lttng-ust."
119 DBG("Got the wait shm fd %d", wait_shm_fd
);
124 DBG("Failing to get the wait shm fd");
130 * Return the wait shm mmap for UST application notification. The global
131 * variable is used to indicate if the the session daemon is global
132 * (root:tracing) or running with an unprivileged user.
134 * This returned value is used by futex_wait_update() in futex.c to WAKE all
135 * waiters which are UST application waiting for a session daemon.
137 char *shm_ust_get_mmap(char *shm_path
, int global
)
139 size_t mmap_size
= sysconf(_SC_PAGE_SIZE
);
140 int wait_shm_fd
, ret
;
145 wait_shm_fd
= get_wait_shm(shm_path
, mmap_size
, global
);
146 if (wait_shm_fd
< 0) {
150 wait_shm_mmap
= mmap(NULL
, mmap_size
, PROT_WRITE
| PROT_READ
,
151 MAP_SHARED
, wait_shm_fd
, 0);
153 /* close shm fd immediately after taking the mmap reference */
154 ret
= close(wait_shm_fd
);
156 PERROR("Error closing fd");
159 if (wait_shm_mmap
== MAP_FAILED
) {
160 DBG("mmap error (can be caused by race with ust).");
164 return wait_shm_mmap
;
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